Most known types of clip-on sunglasses include a pivotable or "flip-up" feature however, those available often times require the user to remove his ordinary spectacles in order to attach the auxiliary or clip-on sunglasses thereto. This is usually accomplished by slipping the top portion of the spectacle frame between one or more pairs of fixed resilient clamping prongs or fingers which form part of the assembly and comprises the flip-up sunglasses. Having to remove ones spectacles to attach the auxiliary sunglasses can be of great inconvenience especially when driving an automobile.
U.S. Pat. No. 3,575,497 issued to LaBlanc illustrates one known type of "flip-up" sunglasses. This configuration for sunglass lenses is adapted to removably clip onto the spectacles in a manner which permits the lenses to be moved between one of two stable positions, an operative position where the sunglasses are positioned within a line of sight and an inoperative position wherein those lenses are in a remote position from the line of sight. In order to position the "flip-up" sunglasses on a users spectacles, the clamping arms are pivoted with respect to one another so as to permit the grasping of the spectacles therebetween. The clamping members are fixedly positioned with respect to one another and an upper region of the clamping mechanism and include a torsion spring which exerts a rotational force against an upper limit of the clamping members in order to clamp the spectacles of the user therebetween. This continued torsional force acting on the clamping mechanisms can often become warn and consequently not provide the requisite torsional force in order to maintain the sunglasses in a fixed position with respect to the spectacles. Furthermore, continued manipulation of the torsional spring and particularly over extension of such a torsional spring can prematurely lessen the life of the flip-up sunglass clip.
In an effort to overcome the aforementioned shortcomings, a clip for mounting sunglass lenses to spectacles is set forth in U.S. Pat. No. 5,164,749 issued to Shelton. Therein, the torsional spring is replaced with a "c" shaped spring which retains the members of the clamping mechanism together and provides the requisite torsional force to the clamping members in order to clamp the sunglass structure to the spectacles of the user. However, again, continued manipulation of the sunglass clip over time will eventually where the "c" shaped spring thus resulting in an inadequate force being applied to the spectacles in order to maintain their position with respect thereto. Additionally, the "c" shaped spring may be easily damaged due to misuse by children should the biasing mechanism be overextended.
Clearly, there is a need in the art for a clip-on sunglass mechanism which may be easily and reliably manipulated by the consumer yet one which resists over flexing and destruction due to misuse.